1. Field of the Invention
The present invention relates to a welding robot which monitors the feedability of welding wire through a welding cable during execution of a welding process.
2. Description of the Related Art
A general welding robot has a welding torch which is attached to a front end part of an arm, a feed device of welding wire which is attached above a third axis of the arm, and a welding cable which connects the feed device and the welding torch. In many cases, the welding cable is laid along an outer surface of the arm with a certain extent of slack. The welding cable has a conduit cable inserted through it. While the welding process is being performed, the welding wire which is fed from the feed device runs through the conduit cable to reach the front end part of the welding torch. Further, the front end part of the welding wire which is exposed from the welding torch is melted by the high heat generated by arc discharge and bonded to the welding base materials so that the welding base materials are welded.
Incidentally, if the curvature of the welding cable becomes greater due to operation of the arm, the curvature of the conduit cable which is inserted through the welding cable also becomes larger. If the welding wire is fed in this state, the outer circumference of the welding wire will strongly rub against the inner surface of the conduit cable, and therefore the feedability of the welding wire through the welding cable deteriorates. Further, due to the damage to the outer surface of the welding wire, the weld quality is liable to fall. Furthermore, due to the inner surface of the conduit cable being abraded, early replacement of the welding cable is required.
To avoid this situation, JP2005-297069A proposes a welding robot where a wire feed device is attached to a base end part of an upper arm part, and a welding cable is stored inside of the upper arm part. In the welding robot of JP2005-297069A, the welding cable is arranged so as to extend in the longitudinal direction of the upper arm part at the inside of the upper arm part, and therefore the amount of deformation of the welding cable as a whole is suppressed. Further, JP2010-36253A proposes the approach of arranging a wire feed device below a third axis of the welding robot so as to reduce the bending of the welding cable as a whole. Further, JP2001-293574A proposes a system comprising a wire feed device which is equipped with servo motors, and a monitor device which calculates a feed resistance of the welding wire by subtracting an estimated torque component from the torque information of the servo motor.
However, even if the welding cable is stored in the upper arm part as in JP2005-297069A, the operating angle of the tilt axis can be considerably large depending on the teaching operation of the welding robot, and therefore the feedability of the welding wire through the welding cable is liable to deteriorate. Further, even if the wire feed device is arranged below the third axis of the welding robot (i.e., by the side of the lower arm part) like in JP2010-36253A, flexure of the welding wire due to operation of the tilt axis can continue to occur. Further, even if a monitor device is used for calculating the feed resistance of the welding wire like in JP2001-293574A, the calculated amount of the feed resistance is affected by the weight of the welding wire which remains at a wire reel, and therefore it is not easy to accurately calculate the feed resistance of the welding wire. Furthermore, there is the defect that the monitor device of JP2001-293574A cannot calculate the feed resistance of the welding wire unless an actual welding process is performed.
A welding robot which can prevent deterioration of the feedability of the welding wire through the welding cable during operation of the arm is being sought.